1. Field
The present invention relates generally to food mixing appliances for domestic use and more specifically to multipurpose electric food mixers specially adapted to mix and knead bread dough in combination with a blender device that utilizes one power source to drive both blender and mixer.
2. State of the Art
In multipurpose kitchen appliances of the type with which the invention is concerned there is typically provided an electric motor secured to a base with a cover attached to the base. The lower end of the output armature shaft of the motor is typically operably attached via a gearbox or pulley to a drive shaft extending through a bottom wall of the mixing receptacle. The upper portion of the drive shaft has a mixing utensil, such as a beater or dough hook, connected to it for mixing a food stuff. The upper end of the output armature shaft of the electric motor is operably attached directly to an impeller means whose impeller shaft extends through the bottom wall of a blender receptacle.
A problem with such prior art devices has been that the cover is not adequately secured to the motor housing so that there is movement of the motor relative to the cover. In the past this problem has been overcome by placing a flexible diaphragm between the base cover and the drive element of the motor which will allow movement of the motor with respect to the cover. This arrangement is undesirable because protection of the motor from spilled liquids depends on the integrity of the diaphragm.
Some of such prior art mixing appliances have been specially adapted to knead dough. A common objective of such dough kneading equipment is to provide desirable dough developing action which develops a network of gluten strands critical to the rising process. The procedure for making dough can be divided into stages. The first stage is to bring about absorption of the liquid ingredients in the dry ingredients, the so-called "pick-up" stage. Next, there is the "clean-up" stage, where materials start to agglomerate. Then, there is the "development" stage, where the gluten in the wheat flour develops and forms a gel as a whole. During development, the gluten in the dough mixture develops a desired cell wall strength to prevent escape of the gas that is trapped in the dough. Such gas retention is required in order to get the desired lightness of the resulting product. While kneading, it is desired to create a pulling action of these gluten strands instead of cutting through such strands. Over-kneading results in a "let-down" stage in which the gluten network breaks down resulting in an undesirably heavy baked end-product.
Hayashi, in U.S. Pat. No. 4,747,690 issued May 31, 1988 and U.S. Pat. No. 4,790,665 issued Dec. 13, 1988, discloses a strain gauge for detecting the progress of kneading in a commercial setting. In addition to measuring strain, temperature and pH of the dough are monitored. The measured strain values along with other measured values are transmitted to a computer control device which compares them to a set of control values. When the measured strain values are within the range of control values at each predetermined measuring point the computer allows kneading to continue. If the measured values deviate from the range of control values, the computer transmits a signal to stop the drive device or calculates a relevant time for subsequent kneading. When the kneading proceeds to a predetermined point in the "development" stage as indicated by the present control values, the computer transmits a signal to stop the drive device.
The problem with this Hayashi system is that it requires development of sets of control values for comparison to the values measured by the probes and sensors. These control values apply to certain types of dough in set amounts. Thus, the equipment is not usable with automatic control over a wide variety of doughs or with variable amounts of dough used in the equipment.
A further problem with domestic dough kneading equipment has been that the entire capacity of the mixing receptacle has not been fully utilizable. Some of the dough hooks employed tend to move the dough upward out of the receptacle and, thus, unnecessarily limit the amount of dough that can be processed in the receptacle. Also, lids that have been provided in the past further limit the capacity of the receptacle.
Another problem with both commercial and domestic devices of the prior art has been action between the dough hooks and the stators. It has been usual to supply a pair of oppositely disposed dough hooks and a pair of corresponding oppositely disposed stators. Since both the stators and the dough hooks are oppositely disposed, the dough balls on the stators are forced through the dough hooks at the same time, thereby producing a doubled amount of drag on the motor.